The findings indicate that the persistence of spike proteins was likely the driver for symptoms of long COVID and post-vaccine syndrome.

Spike protein could remain in immune cells for more than 245 days following vaccination, according to a recent preprint. The study evaluated 50 patients who developed long COVID-like symptoms after the COVID-19 vaccine; none had been infected with the virus.
The authors extracted immune cells from 14 post-vaccine patients and found that 13 had spike protein in their immune cells. Asymptomatic vaccinated people had no spike present.

Researchers from InCellDx, a research company that produces panels and protocols that test for and treat long COVID and post-vaccine syndrome, authored the paper.